1. Field of the Invention
The invention relates to the field of intruder detection systems and, in particular to an inexpensive intruder detection system for small passageways such as air conditioning systems and the like.
2. Description of Related Art
In many facilities, specially those storing government classified materials and the like, it is essential to know that an intruder has attempted to gain entrance, whether or not the attempt was successful. Thus all such facilities incorporate alarm systems to detect intruders such as motion, proximity and sound detectors, in addition to the typical access control. However, these are normally installed in occupied rooms and hallways. In passageways, such as heating and air condition ducts that are not subject to daily inspection, steel bars are installed to prevent access. However, steel bars can be cut and some period of time may pass before normal inspections will detect the break in. In addition, any alarm system for use in such passageways must use incombustible materials because of government fire codes.
Of course motion detectors can be used, but they are expensive and not suited for use in environments where large temperature fluctions occur. Capacitance grids are some times used, however, they must be custom built to fit the particular passageway, must be isolated from the metal wall and can not be made from materials that can burn or cause smoke when subject to the heat from a fire. Thus they are also expensive to manufacture.
Thus, it is a primary object of the invention to provide a system to detect intruders in a passageway.
It is another primary object of the invention to provide a system to detect intruders in a passageway wherein the system is readily adaptable to passageways of varying sizes and shapes.
It is a further object of the invention to provide a system to both detect intruders in a passageway and deter entrance therein.